Many electronic devices are very sensitive to water vapor and oxygen in atmospheric environment, so it is necessary to package the electronic devices to isolate them from external environment. By taking an Organic Light Emitting Diode (OLED) as an example, since an organic material function layer in the OLED is extremely sensitive to water vapor and oxygen, it is necessary to fully isolate the organic material function layer of the OLED from the external environment to make the airtight performance of the OLED meet the requirements (water vapor 10−6 g/da y/m2, and oxygen 10−3 cm3/day/m2), thereby ensuring that the performance of the OLED will not be affected by water vapor and oxygen in the external environment.
It can be seen from the above description that in an environment with low water vapor and oxygen concentrations, a method for testing a package effect of the OLED is also very important. The testing methods that are often used currently mainly comprise a metal oxidation method (i.e., a calcium test method) and a hygroscopic expansion method. The metal oxidation method is a method of quantitatively calculating the water vapor and oxygen concentrations by using changes of transmittance and electrical conductivity of calcium metal under certain water vapor and oxygen concentrations; since this method is a chemical method, its test sensitivity is relatively low. The hygroscopic expansion method can be divided into two types: one is to record a change of an expansion area by using hygroscopic expansivity of a hygroscopic film in combination with a way of camera shooting to thereby implement assessment on the water vapor and oxygen concentrations, however, this method cannot calculate the water vapor and oxygen concentrations accurately; the other one is to dope conductive particles in a hygroscopic film, and measure water vapor and oxygen concentrations by measuring a change of electrical conductivity of the hygroscopic film before and after water vapor absorption, however, this method involves doping conductive particles into a polymer material, and stability and electrical conductivity of the material are both limited to a certain extent, which thus may cause the test result to be not accurate enough.